The long-term goals of the proposed research are: (1) to develop topical treatment procedures which can provide a complete or near complete elimination of both coronal and root surface caries yet do not require continued and/or frequent applications, (2) to develop a reliable in vitro caries test which could reduce the need or cost of clinical trials, and (3) to gain a better understanding of the various physicochemical factors which affect the rates of diffusion of the ions involved in the caries process. The propose research on topical fluoridation will be focused on: (1) improvement of our two-step topical F procedure so that the treatment can increase the permanently bound F content of the tooth to the point that it would be resistant to the level of caries challenge expected in humans, and (2) development of application methods which can effectively deliver the treatment agents to the sites which need the protections against caries the most. In the development of in vitro tests for anticaries treatments by measuring the caries resistance of the treated tooth samples, the following two factors will be given careful consideration: (1) Do the products formed by the treatment withstand the washing action of saliva under normal oral conditions for long periods? and (2) Do the treatment products produce a cariostatic condition in or on the tooth surface rather than a simple physical barrier? A bench scale caries model and a computer simulation of the model will be used to study those factors which my affect caries formation and progression. The results obtained will be used to explore the effects of natural or artificially produced permselectivity of enamel on the rate of lesisn proression in vitro. Our concepts on topical fluoridation of enamel will be applied to studies of the action of F on root surface caries. Differences in the chemical and structural properties of the two tissues will be given careful consideration.